TVK,
A special line... Heh! Many anglers actually use plain floss - almost any floss will do, even dental floss as long as the breaking strength is good enough. You can also find special floss made for the purpose, often just called "dapping floss".
The method is mostly referred to as dapping or blowline fishing, and you should be able to find references to that on the web and if you combine that with the name of author Robert H. Boyle you will most likely find his book on the subject.
Martin
